The mechanism of action of the antineoplastic agent tricyclic nucleoside [TCN; NSC-154020; 3-amino-1, 5 dihydro-5-methyl-1-(B-D-ribofuranosyl)-1, 4, 5, 6, 8 pentaazaace-naphthylene] will be further studied, using chinese hamster ovary cells in culture and a rabbit reticulocyte lysate protein synthesizing system. The length of exposure required to kill cells will be determined; the mechanism of inhibition of purine biosynthesis will be examined; the point of inhibition of protein synthesis will be determined.